Analysis of the efficient induction heating frequency

Abstract

The heating of metal sheets is an important industrial process with various applications, e.g., for the coating and drying of sheets, heat treatments or hot-forming. For these applications, induction heating offers an efficient and clean way to generate the required heat from electrical energy directly inside the sheet. Depending on the orientation of the magnetic field, one distinguishes between longitudinal flux heating, where the magnetic flux is tangential to the sheet surface, and transverse flux heating, where the magnetic flux is normal to the sheet surface. In both configurations, an important design parameter is the frequency of the alternating coil current that creates the time varying magnetic field. Given that the frequency selection drastically affects the system efficiency, this thesis investigates the choice of the optimal frequency to obtain maximum electrical efficiency. To start with, important physical and numerical concepts related to the efficient simulation of induction heating applications will be reviewed. Even though no general three-dimensional analytical solutions are available for sheets due to the absence of rotational symmetries, different two-dimensional approaches will be introduced to gain a deeper understanding of the frequency dependency of the efficiency. Afterwards, two- and three-dimensional numerical results obtained with the Finite Element Method will be compared for both longitudinal and transverse flux heating. Here, investigating the validity of the computationally economical two-dimensional simulations will be of central importance. Moreover, the most important geometry and material parameters will be identified and their influence on optimal frequency and efficiency will be analyzed.